Caption: Western Diamondback Rattlesnakes (Crotalus atrox) inhabit dry, rocky, shrub-covered terrain where they can conceal themselves inside crevices in the rocks or in mouse holes. Crotalus atrox has a plump body, short tail and a broad triangular head. Like all pit vipers, it has a pit organ, which is situated in an indentation of the upper jaw, between the nostril and eye. The pit is about 5 mm deep, with an outer and inner chamber separated by a thin membrane. The membrane senses very slight temperature differences between the snake's inner and ambient temperatures.